Embodiments relate generally to a system and method for sealing a rotary wheel used in HVAC applications, and, more particularly, to a self-adjusting sealing system and method for a rotary wheel used in HVAC applications.
Enclosed structures, such as occupied buildings, factories and animal barns, generally include an HVAC system for conditioning ventilated and/or recirculated air in the structure. The HVAC system includes a supply air flow path and a return and/or exhaust air flow path. The supply air flow path receives air, for example outside or ambient air, re-circulated air, or outside or ambient air mixed with re-circulated air, and channels and distributes the air into the enclosed structure. The air is conditioned by the HVAC system to provide a desired temperature and humidity of supply air discharged into the enclosed structure. The exhaust air flow path discharges air back to the environment outside the structure, or ambient air conditions outside the structure. Without energy recovery, conditioning the supply air typically requires a significant amount of auxiliary energy. This is especially true in environments having extreme outside air conditions that are much different than the required supply air temperature and humidity. Accordingly, energy exchange or recovery systems are typically used to recover energy from the exhaust air flow path. Energy recovered from air in the exhaust flow path is utilized to reduce the energy required to condition the supply air.
Conventional energy exchange systems may utilize energy recovery devices (for example, energy wheels and permeable plate exchangers) or heat exchange devices (for example, heat wheels, plate exchangers, heat-pipe exchangers and run-around heat exchangers) positioned in both the supply air flow path and the exhaust air flow path. A Dedicated Outdoor Air System (DOAS) conditions ambient air to desired supply air conditions through a combination of heating, cooling, dehumidification, and/or humidification.
Rotary wheels represent one type of energy recovery device. A rotary wheel may also be referred to as a rotor, thermal wheel, rotary heat exchanger, enthalpy wheel, heat recovery wheel, desiccant wheel, or the like. In general, a rotary wheel includes a matrix of heat-absorbing or heat/moisture-absorbing material. The wheel is slowly rotated within supply and exhaust streams of an air handling system. During a winter mode of operation, as the rotary wheel rotates, heat and/or moisture is picked up from the exhaust stream in one half of the rotation, and transferred to the supply stream in the other half of rotation. Waste energy from the exhaust stream is transferred to the matrix material, and then transferred from the matrix material to the supply stream, thereby raising the temperature and/or humidity of the supply stream by an amount that is proportional to the temperature and/or humidity differential between the air streams. During a summer mode of operation, the process is reversed, in that energy is transferred from the supply stream to the wheel, and into the exhaust stream, thereby cooling and/or dehumidifying the supply stream before it passes into an enclosed structure.
A typical rotary wheel includes a housing having an internal channel that rotatably retains a wheel. The wheel rotates within the housing to condition supply air. A circumferential or perimeter seal may be secured around a circumference of the channel into which the wheel is rotatably secured. The perimeter seal sealingly engages an outer circumference of the wheel as it rotates within the housing. Thus, the supply air upstream from the rotary wheel in a supply stream is prevented from intermingling with the supply air that is downstream from the rotary wheel in the supply stream. Similarly, exhaust air upstream from the rotary wheel in an exhaust stream is prevented from intermingling with the exhaust air that is downstream from the rotary wheel in the exhaust stream. Without the perimeter seal, air could bypass the wheel and reduce the amount of heat and moisture transfer between the supply air and the exhaust air.
In addition to the perimeter seal, the rotary wheel may also include one or more face seals. The face seals sealingly separate the supply air from the exhaust air.
A brush seal is one type of known face seal. The brush seal is typically resilient and able to adapt to most deviations in the surface of the wheel as it rotates. Typically, the deviations are between 1-4 mm, causing the brush seal to deflect accordingly. However, if the brush seal is too far away from the face, a large surface deviation may cause the brush seal to lose contact with the face of the wheel, thereby causing an air leak.
Higher pressure differentials between supply and exhaust airstreams may force the brush seal away from the face of the wheel, thereby causing the brush seal to deflect and lose contact with the face. Accordingly, air may escape through the gap between the brush seal and the face of the wheel. Clearly, as the brush seal loses contact with the face, the performance of the face seal rapidly diminishes.
Another type of know face seal is a labyrinth seal that is placed proximate a face of a rotary wheel. In order for air to flow through a narrow passageway between a distal end of the labyrinth seal and the face, a large pressure drop is induced. The pressure drop reduces the amount of flow past the labyrinth seal. Typically, labyrinth seals are formed of rubber or plastic. Although labyrinth seals perform well when located very close to the face of the rotary wheel, they do not perform well at greater distances (for example, a distance that exceeds 1/16″ away from the face of the rotary wheel). If the wheel wobbles (that is, vertical run-out), in which the distance from the labyrinth seal to the wheel face varies as the wheel rotates, or if the face has any variation in height, labyrinth seals do not perform well. Yet, the labyrinth seals typically have to be positioned far enough away from the wheel so that they do not come into contact with the wheel as it rotates, which may damage the wheel. Generally, labyrinth seals typically do not contact the wheel. Moreover, because the labyrinth seals are made of materials (such as rubber) that are configured to not damage the wheel if contact does occur, the materials are typically not resilient and often wear down over relatively short periods of time.
Another type of face seal is a contact seal and is typically more effective than a labyrinth seal because it includes a rubber strap, for example, that directly contacts a face of a wheel. Unlike a brush seal, the rubber strap is not porous.
Contact seals typically wear quickly over time because they are formed of materials such as rubber, nylon, or fabric that are generally soft so that they will not damage the wheel. In general, it has been found that typical contact seals wear out and behave like poorly-designed labyrinth seals with increased wear and tear. Most contact seals are susceptible to lifting off the surface of the face of the wheel when exposed to high pressure differentials.